The present invention relates generally to electric coils, and more particularly to a method and apparatus for coating an electric coil.
Workpieces, such as parts of electric motors including armatures, stators, and the like, have electric coils which are often coated with a resin to immobilize together coil windings with adjacent coil windings and immobilize together coil windings with adjacent non-coil structure of the workpiece. For example, when manufacturing armatures, a known coating technique is to trickle a resin onto the wire windings (i.e., the electric coil) of the armature as the armature rotates about its longitudinal axis. Once cured, the resin locks the wires together to reduce excessive vibration of the wire windings when the armature is operating in an electric motor. Without such a coating, or with an incomplete coating having void spaces, excessive vibration of the insulated wire of the wire windings of the electric coil typically leads to a break in the insulation and a shorting out of the electric motor.
In the background section of U.S. Pat. No. 4,160,926, a vat is disclosed which is filled with a varnish, and then the wound stator portion of a motor or generator is immersed in the varnish and removed from the varnish for the varnish coating to polymerize in the atmosphere or in an oven. It is stated that the varnishes can be used in connection with ultrasonic vibration to improve varnish coverage for tight windings or when optimum penetration of the varnish in the shortest period of time is desired.
In U.S. Pat. No. 5,474,799, a liquid resin dispenser is disclosed for coating an electromagnetic coil with resin. Alternating electric current, with a frequency of 25-50 hertz, is supplied to the coil to heat the coil before coating. The alternating current also induces vibration in the coil which promotes migration of the catalyzed resin material into the interstices of the coil. The frequency of the alternating current is selected to promote migration without vibrating the catalyzed resin material off of the coil. It is noted that electric-current heating of the electric coil does not substantially heat the workpiece core and thus fails to promote good resin flow to immobilize together coil windings with adjacent non-coil structure of the workpiece.
In order to prepare the workpieces for the application of resin to the electric coil, the workpieces typically are pre-heated to aid the flow of resin on the electric coil of the workpiece. Preheating the workpieces helps to xe2x80x9cwickxe2x80x9d the resin onto unexposed portions of the coil windings and into the spaces between coil windings and adjacent coil windings and between coil windings and adjacent non-coil structure of the workpieces through a capillary action. In order to more quickly cure the resin, the workpieces typically are post-heated after being coated with the resin.
Workpieces typically are preheated and post-heated by passing the workpieces under radiant heating elements. However, when using radiant heating elements, the distance between the workpieces and the radiant heating elements must be maintained at precise levels to avoid overheating or underheating of the workpieces. Furthermore, the sequence timing (i.e. the residence time of a workpiece underneath a radiant heating element) must be precisely controlled to avoid overheating or underheating of the workpieces. For example, if the conveyor that transports the workpieces must be temporarily shut down for maintenance, overexposure of the workpieces to the radiant heating elements may damage the workpieces.
U.S. Pat. No. 5,401,531 discloses that workpieces can be preheated and post-heated in ovens (before and after trickle coating their electric coils with a resin) by introducing high-temperature, undoubtedly-low-velocity (i.e., less than 50 feet per minute) air into the ovens from blowers and conventional heat exchangers. The blowers are aligned away from the workpieces which travel along a serpentine-shaped conveyor path toward, and away from, the blowers. All exterior surfaces of the workpieces are exposed to air of substantially the same temperature in an oven, and the workpieces require a significant period of time to absorb the ambient heat in an oven. These ovens also requires a relatively large amount of space.
Applicant is aware of an oven used to preheat workpieces (before trickle coating their electric coils with a resin), wherein high-temperature, low-velocity (believed to be less than 50 feet per minute) air enters the oven from a line of spaced-apart holes in a side of a manifold. The workpieces travel, in start-and-stop stages, along a serpentine path in the oven at a constant distance of between 5 and 8 inches from the side of the manifold having the holes. Each workpiece is stopped, in turn, during a same one of the start-and-stop stages, opposite a same one of the holes. It is not known if the workpieces stop opposite any of the other holes. The longitudinal axis of each workpiece is aligned parallel to the central axes of the holes. All exterior surfaces of the workpieces are exposed to air of substantially the same temperature in the oven, and the workpieces require a significant period of time to absorb the ambient heat in the oven. This oven also requires a relatively large amount of space.
Applicant also is aware of ovens in some restaurants which heat a piece of food by blowing high-temperature, high-velocity (i.e., greater than 500 feet per minute) air directly onto the piece of food.
What is needed is an improved method and apparatus for coating an electric coil of a workpiece.
A first method of the invention is for coating an electric coil of a workpiece and includes steps a) and b). Step a) includes applying a curable coating material to the electric coil of the workpiece. Step b) includes externally vibrating the workpiece before the applied curable coating material has cured. Preferably, step b) is performed during step a). Preferably, step b) essentially avoids heating the workpiece.
An embodiment of the invention is apparatus for coating an electric coil of a workpiece. The apparatus includes a mechanism for applying a curable coating material to the electric coil of the workpiece. The apparatus also includes a mechanism for externally vibrating the workpiece before the applied curable coating material has cured. Preferably, the vibrating mechanism externally vibrates the workpiece as the curable coating material is being applied to the electric coil of the workpiece. Preferably, the applying mechanism includes a liquid-resin trickle dispenser, and the vibrating mechanism includes a vibrator operatively connectable to the workpiece.
Several benefits and advantages are derived from the invention. Vibrating the workpiece promotes migration of the coating material into the spaces between coil windings and adjacent coil windings and between coil windings and adjacent non-coil structure of the workpiece. Vibrating reduces void spaces which improves immobilization of coil windings with adjacent coil windings and improves immobilization of coil windings with adjacent non-coil structure of the workpiece. Improved immobilization reduces excessive vibration of the insulated wire of the of wire windings of the electric coil which typically leads to a break in the insulation and a shorting out of the electric motor. Vibrating may decrease the time required for the coating material to saturate the workpiece. Externally vibrating the workpiece, in contrast to internally vibrating (and thus heating) the electric coil by applying an alternating electric current to the electric coil, allows independent and optimal control of workpiece temperature and vibration. Applicants have externally vibrated workpieces (which were pre-heated, but preheating is not considered to be required to obtain benefits from external vibration) during trickle coating of the electric coil of the workpieces, then have cut the workpieces open, and have found the coating on the electric coil showed substantially fewer void spaces than when Applicants trickle coated without external vibration.